1. Diastereomers Stereoisomers:
same molecular formula, same bonding arrangement, different spatial arrangement
Enantiomers:
two stereoisomers that are nonsuperimposable mirror images
Diastereomers:
stereoisomers that are NOT mirror images

2. Diastereomers In general, diastereomers fall into two categories:
geometric isomers
cis-trans
compounds containing two or more asymmetric atoms (but not mirror images)

3. Fischer Projections
Fischer Projections are often used to depict stereochemistry when more than one asymmetric carbon is present.
Left and Right come toward you.
Top and Bottom go away from you.

4. Fischer Projections Rules for using Fischer Projections:
Carbon chain is drawn along the vertical line of the Fischer Projection
C # 1 at the top
asymmetric carbon where the lines cross
Vertical lines:
bonds going away from you
Horizontal lines:
bonds coming towards you

5. Fischer Projections = = = Rules for using Fischer Projections:
Structures can be rotated by 180o only.
Rotation by 90o is NOT allowed.
You cannot flip over a Fischer Projection. = = =

6. Fischer Projections s Fischer Projections are useful when:
drawing mirror images
identifying internal mirror planes of symmetry s

7. Fischer Projections superimposable
Fischer Projections are useful when:
determining if two substances are nonsuperimposable mirror images
remember to follow the rules for using Fischer Projections
rotate 180o
superimposable

8. Stereochemical Relationships
On your exam, you must be able to identify the relationship between two structures.
Different compounds that are not isomers
Same compounds
Enantiomers
Diastereomers

9. Stereochemical Relationships
Different compounds, not isomers:
Different molecular formulas
Structural (constitutional) isomers:
Same molecular formula, different bonding pattern

10. Stereochemical Relationships
Same Compound:
Same molecular formula, same bonding pattern
All sets of equivalent asymmetric carbons will have the same configurations

11. Stereochemical Relationships
Enantiomers:
Same molecular formula, same bonding pattern
All sets of equivalent asymmetric carbons will have the opposite configuration

12. Stereochemical Relationships
Diastereomers:
Same molecular formula, same bonding pattern
At least one set of equivalent asymmetric carbons has the same configuration AND
At least one set of equivalent asymmetric carbons has the opposite configuration

13. Stereochemical Relationships
Example: Determine the relationship between the following pairs of compounds.

14. Identifying All Possible Stereoisomers
A compound with “n” asymmetric carbon atoms can have a maximum of 2n stereoisomers.
Example: What is the maximum number of stereoisomers for each of the following compounds?
2,3-dibromobutane
2,3-dibromo-5-methyloctane

15. Identifying All Possible Stereoisomers
2,3-dibromobutane only has 3 distinctly different stereoisomers:
enantiomers
What is the relationship between the compounds above and below? s s
Same compound

16. Identifying All Possible Stereoisomers
Example: Draw 3-d structures of all possible stereoisomers of 2,3-dichloropentane. Which ones are chiral? Name each one. Give the stereochemical relationship between them.

17. Identifying All Possible Stereoisomers

18. Identifying All Possible Stereoisomers

19. Review
Example: Is the following compound chiral? Name the compound.

20. Review
Example: Is the following compound chiral? What is the maximum number of stereoisomers possible for this compound. Draw one possible diastereomer of this compound.